Efforts to improve upon the performance of natural mineral oil based lubricants by the synthesis of oligomeric hydrocarbon fluids have been the subject of important research and development in the petroleum industry for several decades, leading to recent commercial production of a number of polyalphaolefin synthetic lubricants. These materials are primarily based on the polymerization of α-olefins, such as C2-C20 α-olefins. Industrial research efforts on synthetic lubricants have generally focused on fluids exhibiting useful viscosities over a wide range of temperatures, i.e., having an improved viscosity index (VI), while also showing lubricity, thermal, and oxidative stability and pour point equal to or better than mineral oil. These newer synthetic lubricants provide lower friction and hence increased mechanical efficiency across the full spectrum of mechanical loads and do so over a wider range of operating conditions than mineral oil lubricants.
Well known structural and physical property relationships for polymers as contained in the various disciplines of polymer chemistry have pointed the way to α-olefins as a fruitful field of investigation for the synthesis of oligomers with the structure thought to be needed to confer improved lubricant properties thereon. Owing largely to studies on the polymerization of propene and vinyl monomers, the mechanism of the polymerization of α-olefins and the effect of that mechanism on polymer structure is reasonably well understood, providing a strong resource for targeting on potentially useful oligomerization methods and oligomer structures.
Catalytic polymerization of olefins is a known technique for manufacturing basestocks useful as lubricants. There are various known methods for forming polyalphaolefins in the art, such as for example, U.S. Pat. Nos. 4,827,073; 4,892,851; 4,912,272; 5,012,020; 5,177,276; 5,661,096; 5,731,254; 6,706,828; 6,858,767; and 7,129,197, the entirety of which are incorporated herein by reference. Earlier catalytic polymerization processes used chromium-based catalysts, as discussed in U.S. Pat. Nos. 4,827,073 and 5,012,020, Ziegler-type catalysts, such as titanium trichloride, as discussed in U.S. Pat. No. 5,177,276, and aluminum chloride, as discussed in U.S. Pat. No. 4,912,272. These earlier catalysts gave way to later developed processes using various metallocene catalysts and metallocene catalyst systems, as discussed, for example, in U.S. Pat. Nos. 4,892,851; 5,661,096; 5,731,254; 6,706,828; 6,858,767; and 7,129,197. Such catalyst systems typically comprise the combination of: (a) a metallocene compound, typically a metallocene compound that is based on a Group IVb transition metal such as zirconium, and (b) an aluminoxane. Unbridged substituted bis-cyclopentadienyl transition metal metallocene compounds are discussed in U.S. Published Application No. 2007/0043248.
The polyalphaolefins produced by such methods may, for example, be used as lubricants or as lubricant additives, as discussed in U.S. Pub. App. Nos. 2006/0276355; 2007/0289897; and 2007/0298990, the entireties of which are incorporated herein by reference.
U.S. Pat. No. 6,858,767 discloses that a liquid polyalphaolefin homo- or copolymer, preferably 1-decene, which is substantially amorphous is obtained by a polymerization process employing hydrogen and a particular type of metallocene catalyst. Additionally, liquid polyalphaolefin homo- or copolymer containing from 2 to about 12 carbon atoms possess a unique combination of properties, i.e., low molecular weight (Mw), low polydispersity index (Mw/Mn), controllable kinematic viscosity (Kv100), low Iodine Number (I2) and low glass transition temperature (Tg) and are substantially amorphous. The liquid polyalphaolefin homo- or copolymers are useful for manufacturing a variety of products including lubricating oils in which the polyalphaolefin functions as a viscosity modifier.
U.S. Pat. No. 7,129,197 discloses that one or more oligomers of an olefin are prepared in the presence of a single-site catalyst. Preferably, the olefin is an α-olefin, and the oligomer is a poly-alpha-olefin (PAO). The PAO so prepared is completely or substantially free of tertiary hydrogen resulting from isomerization. Consequently, the PAO possesses improved biodegradability, improved oxidation resistance, and/or a relatively higher viscosity index. The PAO has many useful applications, such as a component of a lubricant.
U.S. Pat. No. 5,177,276 discloses an alpha-olefin oligomer consisting essentially of repeating units having the structural formula:
wherein x represents an integer from 3 to 11, inclusive; and y represents the number of repeating units in the oligomer such that the weight average molecular weight is from about 5,000 to about 20,000; said oligomer having from about 70 to 100 percent head-to-tail alignment of the repeating units of the oligomer. Preferably the weight average molecular weight of the oligomer is from 5,000 to about 10,000; and said oligomer is further characterized as having a dispersity of less than about 5.5, and a Z average molecular weight of less than about 24,000. Additionally, U.S. Pat. No. 5,177,276 discloses recycling unconverted feed, which usually contains saturated alpha-olefin, to the oligomerization process to serve as the reaction solvent.
U.S. Pat. No. 5,731,254 discloses a syndiotactic polyolefin is obtained in a high yield by polymerization or copolymerization of an olefin of the formula Ra—CH═CH—Rb in the presence of a catalyst consisting of a metallocene of the formula I
in which M1 is titanium, zirconium, vanadium, niobium or tantalum, and an aluminoxane. This polyolefin has a very high molecular weight, a very narrow molecular weight distribution and a very high syndiotactic index. Shaped articles produced from the polymer are distinguished by a high transparency, flexibility, tear resistance and an excellent surface gloss.
U.S. Pat. No. 4,892,851 discloses a metallocene catalyst for use in preparing syndiotactic polyolefins. The catalyst comprises a bridged metallocene in which one of the cyclopentadienyl rings is substituted in a substantially different manner from the other ring. It was discovered that this type of catalyst is highly syndiospecific, and it also produces a polymer with a novel microstructure. The invention further includes the use of one or more of the catalysts in a polymerization process. The catalyst is generally described by the formulaR″(CpRn)(CpR′m)MeQk wherein each Cp is a cyclopentadienyl or substituted cyclopentadienyl ring; each Rn and R′m is the same or different and is a hydrocarbyl radical having 1-20 carbon atoms; R″ is a structural bridge between the two Cp rings imparting stereorigidity to the catalyst; Me is a group 4b, 5b, or 6b metal from the Periodic Table of Elements; each Q is a hydrocarbyl radical having 1-20 carbon atoms or is a halogen; 0≦k≦3; 0≦n≦4; 1≦m≦4; and wherein R′m is selected such that (CpR′n) is a sterically different ring than (CpRn).
U.S. Pat. No. 4,827,073 discloses a process for oligomerizing alpha olefin to produce lubricant range hydrocarbon stock including the step of contacting said alpha olefin with a supported solid reduced Group VIB (e.g., chromium) catalyst under oligomerization conditions at a temperature of about 90° to 250° C. to produce liquid lubricant hydrocarbon. The product comprises the polymeric residue of linear C6-C20 1-alkenes, said composition having a branch ratio of less than 0.19. The weight average molecular weight is between 420 and 45,000, number average molecular weight between 420 and 18,000, molecular weight distribution between 1 and 5 and pour point below −15° C. The hydrogenated lubricant range hydrocarbon product has viscosity index of about 130 to 280 and viscosity up to about 750 cS. The process is particularly useful where the starting alpha olefin consists essentially of olefinic hydrocarbon having 8 to 14 carbon atoms or mixtures thereof; wherein the process conditions include reaction temperature of about 100° to 180°; and wherein the support catalyst includes porous inert silica.
U.S. Pat. No. 5,661,096 discloses Ziegler catalysts based on a metallocene as the transition metal component and an aluminoxane as the activator, preactivation of the metallocene with the aluminoxane results in a considerable increase in the activity of the catalyst system. Furthermore, 1-olefin polymers of a high degree of isotacticity and having compact, spherical particles, a very narrow particle size distribution and a high bulk density are obtained by means of a catalyst system of this type.
U.S. Pat. No. 5,012,020 discloses a novel composition is disclosed that is particularly useful as a lubricant viscosity index improver. The composition comprises branched branched C30-C10000 hydrocarbons that have a branch ratio of less than 0.19 and viscosity at 100° C. between 725 CS and 15,000 cS. The novel compositions comprise the product of the oligomerization of C6 to C20 alpha-olefin feedstock, or mixtures thereof, under oligomerization conditions at a temperature between −20° C. and +90° C. in contact with a reduced valence state Group VIB metal catalyst on porous support. The compositions have viscosities at 100° C. between 725 cS and 15,000 cS. Using the foregoing compositions in admixture with mineral oil and synthetic lubricants provides novel lubricant blends that show an elevated viscosity index. The mixtures also show an increased stability to shear stress at high temperature with all blends notable by exhibiting Newtonian flow.
U.S. Pat. No. 4,912,272 discloses a lubricant mixtures having unexpectedly high viscosity indices. The mixtures are blends of high viscosity index polyalphaolefins (HVIXPAO) prepared with activated chromium on silica catalyst and polyalphaolefins prepared with BF3, aluminum chloride, or Ziegler-type catalyst. Superior blends are also prepared from HVIXPAO with mineral oil and/or other synthetic liquid lubricants.
U.S. Pat. No. 6,706,828 discloses a process for the preparation of a poly(α-olefin) polymer wherein the process comprises polymerizing at least one α-olefin in the presence of hydrogen and a catalytically effective amount of catalyst comprising the product obtained by combining a metallocene catalyst with a cocatalyst, the metallocene catalyst being at least one meso compound of general formula:

wherein: A1 and A2 are independently selected from the group consisting of mononuclear and polynuclear hydrocarbons;
M1 is a metal from group IVb, Vb, or VIb of the Periodic Table;
R1 and R2 are independently selected from the group consisting of hydrogen, C1-C10 alkyl, C1-C10-alkoxy, C6-C10 aryl, C6-C10 aryloxy, C2-C10 alkenyl, C7-C40 arylalkyl, C7-C40 alkylaryl, C8-C40 arylalkenyl and halogen;
R7 is selected from the group consisting of:
═BR11, ═AlR11, —Ge—, —Sn—, —O—, —S—, ═SO, ═SO2, ═NR11, ═CO, ═PR11 and ═P(O)R11, where
R11, R12, and R13 are independently selected from the group consisting of hydrogen, halogen, C1-C10 alkyl, C1-C10 fluoroalkyl, C6-C10 aryl, C6-C10 fluoroaryl, C1-C10 alkoxy, C2-C10 alkenyl, C7-C40 arylalkyl, C8-C40 arylalkenyl, and C7-C40 alkylaryl, or R11 and R12 or R11 and R13, in each case with the atoms connecting them, form a ring; and M2 is selected from the group consisting of silicon, germanium, and tin;
R8 and R9 are independently selected from the group consisting of hydrogen, halogen, C1-C10 alkyl, C1-C10 fluoroalkyl, C6-C10 aryl, C6-C10 fluoroaryl, C1-C10 alkoxy, C2-C10 alkenyl, C7-Cao arylalkyl, C8-C40 arylalkenyl, and C7-C40 alkylaryl; m and n are identical or different and are zero, 1, or 2, with m plus n being zero, 1 or 2.
Regardless of the catalyst system and process parameters employed, it has been difficult to directly produce lower viscosity range polyalphaolefins, e.g., polyalphaolefins having a viscosity of approximately 100 cSt or below, without incurring lower selectivity and yields due to the simultaneous production of higher viscosity byproducts and higher molecular weight oligomers and polymers. Thus, a significant problem in the manufacture of synthetic lubricants is the production of lubricants in a preferred viscosity range at high selectivity, and yield, as well as conversion. Thus, the need exists for processes and reaction systems for forming polyalphaolefins of desired lubricant viscosity at high conversion, selectivity and yield.